This is correct finish of exhaust manifold fasteners for 1969 340, and is most likely correct for 1968 318. AFAIK the difference between 318 and 340 exhaust manifold fasteners is just the length of the long hex nuts?

6 hex bolts, 4 hex nuts, 6 studs, all phosphated.

2 long hex nuts and 6 conical washers, all bare metal. The thick conical washers were stamped from steel plate with mill scale on both sides, so the washers also have mill scale on the top and bottom faces with bare metal on the edges.

Of course the final finish was engine paint.

You can verify these finishes by researching AMKproducts.com catalog. They offer a 318 kit of all these fasteners, Part No. C-8062 on page 6 here